Portable surfacing machine for terrazzo floors



C. 17, 1967 R L BREJCHA ET AL v3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March l, 1965 4Sheets-Sheet 1 mw/W ATTORNEYS @Ct 17, 1967 R. J. BREJCHA ET AL 3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March l, 1965 4Sheets-Sheet 2 N VEN TOR.

[gy-:2% l: l a Y ATTORNEYS @Cil 17, lg' R, 1 BREJCHA ET AL 3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March v1, 1965 4Sheets-Sheet ,5

C. 17, 1967 R BREJCHA ET AL 3,347,596.

PORTABLE SURFACING .MACHINE FOR TERRAZZO FLOORS Filed March i, 1965 4sheets-sheetv 4 N RN . N pi mm? g ATTORNEYS*- 3,347,596 PORTABLESURFACING MACHINE FOR TERRAZZO FLOORS Robert J. Brejcha, Westchester,Narciso G. Modesto, Morton Grove, and Wayne F. Ridenour, Chicago, Ill.,assignors, by mesne assignments, to General Stone and MaterialsCorporation, Roanoke, Va., a corporation of Virginia Filed Mar. 1, 1965,Ser. No. 435,958v 7 Claims. (Cl. 299-10) The present invention relatesto an improved method and apparatus for rough finishing cementitiouscast surfaces, such as Portland cement, concrete, and the like, and hasparticular reference to the finishing or surfacing of terrazzo floors.

The art of terrazzo floor finishing has changed little in the hundredsof years which have elapsed since the art was developed. Basically, theprocedure consists in casting a dispersion of marble chips in Portlandcement along the supporting surface, trowelling the surface, and settingit by hydration of the cement. Then, the surface is abraded until thedesired surface -nish is obtained. About the only concession to moderntechnology which has taken place in this art is the substitution ofpower driven abrasive blocks or rollers for the manually operatedabrasive stone mounted on a long handle which had theretofore beenemployed.

The present commercial method of rough finishing terrazzo consists ofrubbing blocks of a silicon carbide abrasive over the cast terrazzosurface under high unit pressure, in the presence of water which servesas a coolant and prevents filling or clogging of the blocks with theabraded product. The blocks are attached to rotating arms of a weightedportable machine which is maneuvered over the surface of the fioor in arandom pattern by the machine operator. The terrazzo is graduallyabraded from the surface, to a depth usually .measuring about 2 mils perpass, and forms a thick slurry when it combines with the Water coveringthe surface being finished. The condition of the surface is continuallyobserved by the operator who must judge when a sufficient depth has beenreached to expose the largest proportion of marble chips to cementbinder. As a given portion of the door is finished, the operator movesto the next adjacent section and repeats theoperation While blending the-ground surfaces of the two sections.

Walls which have been previously finished are normally protected with aplastic film to prevent them from being splashed with the slurry. Nearbymetal trim similarly must be protected from the slurry since it is quitecorrosive in nature. Because of thelarge quantities of Water employed,the floors are normally completed in a newly erected structure beforeceiling tiles are incorporated, to prevent moisture damage to the tiles.

Following the finishing operation, the floor is scraped in an attempt toremove .a portion of the slurry and also to move the major bulk of it toa location where it may dry out and from which it can be removed byshoveling. This clean up operation involves a substantial amount of timeand labor and adds significantly rto the cost of the entire finishingoperation.

Beside the disadvantages which are inherent in the process presentlyused due tothe necessity for using large volumes of water, the presentlyused commercial process is quite slow, since it is usually desirable to,remove about 40 mils from the floor, and this takes an average of about20 passes with presently available equipment. Furthermore, the operationas presently practiced can only be performed on a partially cu-redterrazzo floor which has been cured for less than'9 days. After thattime, the abrading action becomes ineffective in removing surface mate-United States Patent O rial. This requirement demands careful schedulingof the entire terrazzo installation from pouring to finishing.

One of the largest machines presently commercially available for thisoperation includes 12 abrasive blocks which operate at about a 71/2horsepower demand. This machine is able to rough finish terrazzo at arate of approximately 500 square feet in an eight-hour day. This isaccomplished with the use of two complete sets of abrasive blocks, a newset being installed for operation at the beginning of the working dayand replaced at the middle Iof the day with a new set.

The present invention is directed to an entirely difierent concept inrough finishing of cementitious materials, particularly terrazzotloorsurfaces. It does not rely upon abrading, but rather employs a cuttingaction resulting in the milling of the surface to a predetermined,controllable Idepth so that the fioor is cut in a single pass to therequired depth. The process is entirely dry, rendering removal of finesmore convenient without the clean up difiiculties which are encounteredin conventional terrazzo finishing processes. What is more, thefinishing of the floor is accomplished at substantially lower powerrequirements than presently employed commercial operations.

The heart of the cutting mechanism of the machine of the presentinvention consists of a pair of counter rotating wheels, each of whichhas a plurality of hard cutter elements spaced along the peripherythereof, the two wheels being driven from a common drive source, withtheir projecting cutter elements being at interdigitated relationship.The two cutter wheels thus cut overlapping paths or tracks to apredetermined depth, depending on the elevation of the wheels. Themachine is propelled in the forward or cutting direction by means of aframe supported on a plurality of wheels, typically a set of threewheels, two of which are located on one side of the machine, and thethird on the opposite side to provide a datum planeqforvthe cuttingaction. The third Wheel is made vertically adjustable with respect tothe other two, to provide an adjustable three point suspension systemfor the machine. To initiate material removal, the cutter wheels areslowly lowered vertically into the surface of the material to therequired cutting depth, and forward driving motion is imparted to thewheels. To this end, each of the wheels is preferably provided with itsown drive motor. With the tool elements equally spaced on the Wheelperipheries, and with the rotational speed and horizontal travel heldconstant, each cutter element then removes an equal amount of materialfor each rotational pass.

The basic mechanism of material removal in accordance with the presentinvention is failure of the material by the process of shear due toloads imposed by the cutting element. When ductile metals are cut inthis manner, a continuous chip is formed since the shear deformationoccurs without fracture of the metal. In that case, the metal deforms byshear in a narrow zone extending from the tool cutting edge to the worksurface. In the case of low ductility or brittle materials, such as inthe case of cement and terrazzo mixtures, a discontinuous chip results.The discontinuous chip is formed because the material is not able toundergo the required amount of shear deformation without fracture, andtherefore the fracture occurs intermittently along the shear plane,breaking the chip into small segments.

An object of the present invention is to provide an improved machine forsurfacing terrazzo surfaces and the like without the use of an abradingtype action.

Another object is to provide a completely dry finishing process of thetype described.

Another object of the invention is to provide an improved portableterrazzo surfacing machine in which the. depth of cut can be preciselycontrolled, and succeeding cuts can be blended together to form auniformly finished surface.

A further object is to provide a finishing method for terrazzowhich canbe used after extended curing times.

Still another `object of the invention is to provide a machine forsurfacing floors of the type described which is capable of substantiallygreater productivity than comparable machines used in the past, and doesnot involve extensive clean-up.

Another object ofthe invention is to provide a machine for surfacingcementitious floors and the like which operates at lower powerrequirements for the same amount of surface removal.

Still another object of the invention is to provide an improved cutterwheel design for the milling of cementitious surfaces and the like toprovide a precise cut to a predetermined depth.

Still another object of the invention is to provide an improved cuttingwheel assembly which provides a milling action rather than an abradingaction on a terrazzo oor.

Another object of the invention is to provide an improved method forsurfacing terrazzo surfaces and the like enabling succeeding cuts to beprecisely matched.

A further description of the present invention will be made inconjunction with the attached sheets of drawings which illustrate apreferred embodiment thereof.

In the drawings:

FIGURE l is a bottom plan view of the machine, particularly illustratingthe configuration of the cutting wheels;

FIGURE 2 is a side elevational view of the machine;

FIGURE 3 is another side elevational view of the machine;

FIGURE 4 is a top plan view of the machine;

FIGURE 5 is a view partly in elevation and partly in cross-section ofthe machine showing the drive elements more specifically;

FIGURE 6 is a fragmentary view in perspective of a single cutting`element, illustrating its orientation with respect to the remainder ofthe cutting wheel for proper cutting action;

FIGURE 7 is a fragmentary view in elevation illustrating the positionofthe cutting elements `during the first cut provided by the machine;

FIGURE 8 is a view similar to FIGURE 7 but showing the position of theelements prior to the start of a succeeding cut; and

FIGURE 9 is a view similar to FIGURES 7 and 8 and showing the positionof the elements during succeeding cuts.

As shown in the drawings:

In FIGURE l, reference numeral 10 indicates generallya main framesupported for forward movement in the cutting direction by means of aset of wheels consisting of substantially coplanar wheels 11 and 12secured to one side of the frame, and a `vertically positionable drivewheel 13 secured centrally of the opposite side of the main frame 10.Each of the drive wheels 11, 12 and 13 has an associated drive motor,14, `16 and 17 respectively, therthree motors being driven insynchronization. The drive wheels 11, 12 and 13 are resilientlysurfaced, being composed of a hard rubber `tire having a Durometer Areading of about 80 to 90. The tires are made resilient so that they canride over slight surface irregularities without significantly changingthe machine elevation.

A sub-frame 18 is carried by the main frame 10 in vertically adjustablerelationship, and the sub-frame 18 carries a pair of4 cutter wheels 19and 21 which provide the cutting action in a cutting plane. As bestillustrated in FIGURE 1, the cutter wheels 19 and 21. each carry aplurality of equally peripherally spaced cutting elements 22, thecutting elements 011` the wheel 19 being in inter' digitatedrelationship with the cutting elements on the wheel 21. The cuttingelements 22 are preferably cotilposed of a hard material such astungsten carbide. Specifically, we prefer to employ the commerciallyavailable material known as Carboloy 999 since it has excellent heat,abrasion, and wear resistance. This material is composed of about 97%tungsten carbide and 3% `c0- balt by weight. It is `formed by blendingthe powdered materials in proper proportions, compacting them underextremely high pressures lin a die, and sintering them into a solidpiece. The final density of the product is about 15.25 grams per cubiccentimeter, and `its hardness, as measured on the Rockwell A scale is92.7.

The manner of securing the cutting elements 22 to the cutter wheels19and 21 is preferably one which permits rapid release of the cuttingelements for purposes of reorientation or replacement. We have found itparticularly effective to use the tool geometry and type knowncommercially as Carb-O-Lock, marketed by the General Electric Companywhich permits rapid tool changeover by means of a quick action lockingprinciple for rigidly retaining the carbide inserts, and an insertdesign which is shaped geometrically to offer a large` number of cuttingedges so that a new cutting edge can be presented to the work byrepositioning the cutter element 22 in its socket with a sharp cuttingedge presented to the'work.

The orientation of the cutter element 22 with respect to the plane ofthe wheel in which it is located is best illustrated in FIGURE 6 of thedrawings. In the particular embodiment there illustrated, the cutterelement 22 taxes the form of Va generally square plate having roundedcorners 23, typically with 'a radius of 1/16 inch. With this type ofcutter element, the eight edges; provide cutting surfaces which can bepresented to the work merely by embodiment there illustrated, the cutterelement 22 taxes respect to its associated cutter wheel.

In FIGURE 6, the axis of the cutter wheel is indicated at referencenumeral 24, and a reference radial plane extending from the centerlineof the cuttingwheel is represented by reference numeral 26. In order toachieve the proper type of cutting action, the cutting element 22 ispositioned so that it has a negative radial rake with respect to theradial plane 26, the rake in this direction being defined by the `anglea. The cutter element 22 should also have a negative axial rake,represented by the angle b. The corner angle, represented by reference cis not particularly critical, but should be less than for a squareshaped insert, otherwise the adjacent or bottom side of the insert woulddrag over the finished surface and a propercut would not be made. Inpractice, it was found that negative rake angles a and b should be onthe order of 5, while75 vis appropriate for the corner angle c.

Referring to FIGURE 5, it will be seen that the cutter wheels 19 and 21are fitted to shafts 27 and 28, respectively, by means of tapered matingdiameters indicatedy at 29 and 31 respectively, The wheels 19 and 21 areretained on the shafts by means of locking bolts 32. The

cutter wheels 19 and 21 are of sufcient mass to act as flywheels todrive smoothly through` load uctuations without creating excessivevibrations.

The ends of the shafts 27 and 28 are mounted between bearings 34 and 35,and bearings'36 and 40 respectively. To the `center of each shaft thereis mounted a worm gear 37 and 38 respectively. The worm gearsy 37 and 38are driven by a central worm 39 which, in turn, is driven from a belt 41trained about a pulley 42 connected to the drive shaft of a cutter drivemotor 43 carried by the subframe 18. The two cutter wheels 19 `and 21are thereby drivenat identical speeds in opposite directions.

The cutter wheels, the worm gear drive, and the motor assembly areconnected to the main frame '10 by means of jack screws 46, 47, 48 and49 received in suitable bearings (not shown) in the main frame 10. Eachof the jack screws 46 through 49 inclusive is rotated by means ofassociated sprockets 51, 52, 53 and 54 respectively. About the sprocketsthere is trained a chain 56 which is driven from a drive sprocket 57connected to a drive shaft S8 of a drive motor 59 (see FIGURE 5). Anidler sprocket 61 is provided to adjust the tension on the chain 56. Thedrive system is such as to position the sub-frame 18 in one of the twopositions with respect to the main frame 10, namely, a retractedposition in which the cutter elements 22 are elevated slightly withrespect to the plane or suspension provided by the drive wheels (seeFIGURE 8), or in a cutting position in which the cutter wheels 19 and 21are set to the predetermined cutting depth required for each pass of themachine (see FIGURE 7).

The drive wheel 13 is driven by means of a bevel gear 63 secured to adrive shaft 65 as best illustrated in FIGURE 5 of the drawings. Thewheel 13 rotates about a shaft 64 and has a bevel gear portion 70engaging the bevel gear 63. The shaft 64 has a vertical portion 66provided with a rack 67 engageable by a gear 68. The latter is driven bya motor 69 to position the wheel 13 at the proper elevation so that itprovides a substantially horizontal datum cutting plane for the cutterwheels when the wheels 11, 12 and 13 are in the cutting position.

The nes produced by the milling operation are drawn into the hollowcenters of the shafts 27 and 28 respectively by providing passages 71and 72 respectively in the cutter wheels 19 and 21. The hollow shaftsare in communication with a pair of liexible ducts 73 and 74 which vareconnected to the inlet side of a blower 76 operated from the main drivemotor 43. The blower discharges into a conduit 77 which delivers thefines to a collector 78 which may consist of a conventional bag typelter mounted over the top of the main framework. In order to increasethe velocity of the air which flows past the cutter elements 22, it isdesirable to put a shroud or skirt 79 surrounding the base of the mainframe, as best illusstrated in FIGURE 2 of the drawings. The airmovement within the shroud is of suicient velocity to carry the residuallines or chips into the air stream and up to the lter elements in thecollector 78.

The controls for the unit are located in a control box 81 connected tothe machine by means of a flexible cable 82. Also coming into themachine is a liexible power cable 83 as illustrated in FIGURE 5. Themain power cable and the'control cables from the unit are taken oli atone side to enable the operator to conveniently control the cable-andkeep it from the path of the cutters. All controls are handled by asingle control box 81 without a rigid connection to the nishing machine.

At the completion of one cutting pass, the machine must be movedlaterally in order to position it for the cutting of the next trackadjacent to and merging with the track previously cut. For this purpose,there is provided two additional pairs of wheels identified at referencenumerals 84, 85, 86 and 87 in the drawings. These wheels are rotatablymounted on shafts which are received within housings designated atreference numerals 88, 89, 90 and 91 respectively. Means (not shown) areprovided within the housings 88 through 91, inclusive, to raise andlower the wheels, and to drive them in the lateral direction. In theirretracted position, as illustrated in FIGURES 2 and 3 of the drawings,the wheels 84 to 87 are raised from contact with the oor line, so thatthe weight of the machine rests on the three drive wheels 11, 12 and 13.With the wheels in their extended position, however, the weight of themachine rests on the wheels 84 to 87, and the drive wheels 11 to 13inclusive are raised above the level of the floor so that the machinecan be moved laterally to the next adjacent cutting path.

The sequence of operations involved in surfacing a floor is lbestillustrated in the showings of FIGURES 7 to 9 inclusive. In position forthe starting cut, the cutter wheels 19 and 21 are fully retracted intotheir completely retracted position, so that they are clear of the floorgenerally indicated at F. The adjustable drive wheel 13 is also in itsuppermost position relative to the main frame and the weight of the unitrests on the three drive 6 wheels 11, 12 and 13. The contact areas ofthese three drive wheel tires then all lie in a single datum plane whichis parallel to the cutter faces.

With the three drive wheels at rest, the cutter wheels 19 and 21 'arerotates at standard cutter speeds. The filter system contained in thecollector 78 starts operating with the cutter wheels 19 and 21. Thevertical cutter actuators driven by the chain r56 are energized, and thecutters lower gradually to lower the cutting plane to a predetermineddepth, usually on the order of 40 mils below the surface F, asillustrated in FIGURE 7 of the drawings. When the cutters reach thisposition, the forward feed motion begins by the operation of the threeVsynchronized drive motors 14, 16 and 17. The forward motion continuesuntil the operator manually stops the action, at which time, the cutterwheels 19 and 21 may be manually or automatically retracted to the fullclearance position.

Assuming that the following machining pass will be made parallel andadjacent to the first pass, the operator then lowers the lateral drivewheels 84, 85, 86 and 87 until the unit is raised from the floor, andall of the weight of the unit rests on these four wheels. The unit isthen moved laterally along on these wheels until it reaches a positioncomparable to that shown in FIGURE 8 wherein the two drive wheels 11 and12 will (when lowered) come to rest on the uncut surface, while thevertically adjustable wheel 13 will come to rest in' the track 93 cut bythe previous pass. Then, the actuator for the vertical adjustment of thedrive wheel 13 is energized, namely, the motor 69 which drives thegear'68 to lower the wheel 13a distance equal to the depth of theprevious cut. When the unit is then finally lowered s0 that the entireweight is again on the three drive wheels, the cutting plane of thecutter wheels will again be near horizontal. When the cutter wheels areagain actuated vertically downwardly to cut to the same depth as theprevious track, as illustrated in FIGURE 9, the new cut will blend withthe previous cut. With the lowering of the cutters 19 and 21, the cycleis once again repeated, except that for all additional passes, thesingle drive wheel 13 need not be vertically adjusted since allsucceedng cuts will be repetitions of the second c`ut described inconjunction with FIGURES 8 and 9.

Cutter yspeed should be correlated with feed rate to secure an adequatespeed while still maintaining a reasonabletool life. Our tests lhaveshown that when a Carboloy 999 cutter point was operated at a speed ofapproximately 272 feet per minute (linear speed of the cutting element)and a feed rate of 0.0115 inch per tooth was used, it produced a surfacecondition which could be easily polished out, and that the tool lifeunder these conditions was about 4 hours, an acceptable gure. Testsindicated that the power to produce such a cut was below 0.1 horsepowerper cubic inch per minute of material removed. It was also determinedthat the curing time or aging of the terrazzo from periods varying from4 days to 30 days had little or no effect upon the tool life or theother cutting parameters.

At the above operating conditions, using two cutter wheels each of onefoot in diameter and having l2 carbide cutting elements, the cutterwheels would be operated at approximately 87 r.p.m., and at a forwardfeed rate of about 12.0 inches per minute. This results in a surfaceremoval rate of about 2 square feet per minute, and a volume removalrate of about 11.5 cubic inches per minute, assuming the depth of cut tobe 0.040y inch. At this rate, the surface area finished in 8 hour ofoperation is about 960 square feet. It is estimated that the aboveoperation requires less than 1.2 horsepower, a figure considerably lessthan that employed in the abrading type machines presently in use.

It should be evident that various modifications can be made to thedescribed embodiments without departing from the scope of the presentinvention.

We claim as our invention:

1. A machine for surfacing terrazzo surfaces and the like comprising amain frame, a pair of drive wheels at one end of said frame, a thirddrive wheel mounted on the opposite end of said frame, each of saidwheels having resilient surfaces thereon, means for changing theelevation of said third wheel with respect to said pair of drive wheels,means for driving the three drive wheels, a subframe carried by saidmain frame, a pair of cutter wheels mounted on said sub-frame, means forvarying the elevation of said sub-frame relatively to said main frame, aplurality of additional wheels carried by said main frame, means forraising and lowering said additional wheels lto engage the surface beingworked and ,thereby raise said three drive wheels `oi said surface topermit lateral movement of said machine on said additional wheels andpermit retraction of said additional wheels so that said surface isengaged py the three driven wheels;

2. A machine for surfacing terrazzo surfaces and t-he like comprising amain frame, a plurality of resilient drive wheels on said main frame forpropelling said frame in a forward direction, `means for adjusting theelevation of one of said drive wheels with respect to the others, aplurality of retractible wheels for propelling said main frame in alateral direction, a sub-frame carried by said main frame, means forpositioning said sub-frame vertically with respect to said main frame, apair of cutter wheels carried by said sub-frame and rotatable alongparallel vertical axes, each of said cutter wheels having a plurality ofcutter elements peripherally spaced thereon, with the cutter elements ofone wheel being in interdigitated relation with respect to the cutterelements of the other, and a common drive meansy for said cutter wheelsmounted on said subframe.

3. The machine of claim 2 which includes a separate drive. motor foreach of said drive wheels.

4. The method of surfacing a terrazzo iioor or the like which comprisessupporting a cutting mechanism on three wheels which ldeiinea horizontaldatum cutting plane, said cutting mechanism including a pair of counterrotating wheels each having peripherally spaced cutting elements thereonoriented such that each element provides a -point cut along the surface,lowering said wheels while rotating the same to cut said floor `to apredetermined depth, moving the wheels forwardly to thereby cut a trackof said predetermined depth, raising the cutter wheels out of cuttingengagement with said oor, moving said cutting mechanism laterally sothat at least one of said wheels rests on an uncut surface while theremaining wheels rest on the previously cut track, lowering saidremaining wheels by the amount of said predetermined depth of cut, andlowering said cutting wheels and moving said machine yforwardly to cut atrack parallel to the first track and having substantially the samedepth of cut. 5. A machine for surfacing terrazzo surfaces and the likecomprising: a main frame, drive means on said main frame including atleast three drive wheels at least one of which is selectively verticallyadjustable with respect to said main frame for maintaining alignment ofsaid main frameina datum plane, a sub-frame carried by said main frame,

a pair of cutter wheels mounted on said sub-frameV for counter-rotationon spaced parallel axes, cutter elements on said cutter wheels arrangedfor interdigitated overlapping cutting action in a cutting plane, andmeans for selectively vertically adjusting said sub-frame with respectto said main frame to vary the elevation of the cutting plane withrespect to the datum plane.` 6. The machine as defined in claim 5wherein said drive wheels are comprised of resilient material.

7. The machine as defined in claim 5, each of said cutter elementscomprising a radially extending .plate having a plurality of roundedcutting corners and being j positioned on its respective cutter wheel soas to have a negative radial rake and a negative axial rake with respectto a reference radial plane extending from the` centerline of its cutterwheel.

References Cited UNITED STATES yPATENTS 308,366 l1/1884 Maloy 125--51,647,066 10/ 1927 Westman ,299-25 XRv 1,812,771 6/1931 Blood et al.299-41 2,584,738 2/1952 Reitz 299-39 X 2,769,626 11/1956 Becker 299-412,923,107 2/'1960 Biasoni 51-1177 3,102,372 9/1963 Vezner 51-177 ERNESTR. PURSER, Primary Examiner.

4. THE METHOD OF SURFACING A TERRAZZO FLOOR OR THE LIKE WHICH COMPRISESSUPPORTING A CUTTING MECHANISM ON THREE WHEELS WHICH DEFINE A HORIZONTALDATUM CUTTING PLANE, SAID CUTTING MECHANISM INCLUDING A PAIR OF COUNTERROTATING WHEELS EACH HAVING PERIPHERALLY SPACED CUTTING ELEMENTS THEREONORIENTED SUCH THAT EACH ELEMENT PROVIDES A POINT CUT ALONG THE SURFACE,LOWERING SAID WHEELS WHILE ROTATING THE SAME TO CUT SAID FLOOR TO APREDETERMINED DEPTH, MOVING THE WHEELS FORWARDLY TO THEREBY CUT A TRACKOF SAID PREDETERMINED DEPTH, RAISING THE CUTTER WHEELS OUT OF CUTTINGENGAGEMENT WITH SAID FLOOR, MOVING SAID CUTTING MECHANISM LATERALLY SOTHAT AT LEAST ONE OF SAID WHEELS RESTS ON AN UNCUT SURFACE WHILE THEREMAINING WHEELS REST ON THE PREVIOUSLY CUT TRACK, LOWERING SAIDREMAINING WHEELS BY THE AMOUNT OF SAID PREDETERMINED DEPTH OF CUT, ANDLOWERING SAID CUTTING WHEELS AND MOVING SAID MACHINE FORWARDLY TO CUT ATRACK PARALLEL TO THE FIRST TRACK AND HAVING SUBSTANTIALLY THE SAMEDEPTH OF CUT.